57.7.8.7 Header Reception (Client Node Configuration)
All the LIN frames start with a header which is sent by the host node and consists of a Synch Break Field, Synch Field and Identifier Field.
In client node configuration, the frame handling starts with the reception of the header.
The USART uses a break detection threshold of 11 nominal bit times at the actual baud rate. At any time, if 11 consecutive recessive bits are detected on the bus, the USART detects a Break Field. As long as a Break Field has not been detected, the USART stays idle and the received data are not taken in account.
When a Break Field has been detected, the FLEX_US_CSR.LINBK flag is set and the USART expects the Synch Field character to be 0x55. This field is used to update the actual baud rate in order to remain synchronized (see Client Node Synchronization). If the received Synch character is not 0x55, an Inconsistent Synch Field error is generated (see LIN Errors).
After receiving the Synch Field, the USART expects to receive the Identifier Field.
When the Identifier Field has been received, the FLEX_US_CSR.LINID flag bit is set. At this moment, the IDCHR field in the LIN Identifier register (FLEX_US_LINIR) is updated with the received character. The Identifier parity bits can be automatically computed and checked (see Identifier Parity).
If the header is not entirely received within the time given by the maximum length of the header tHeader_Maximum, the FLEX_US_CSR.LINHTE error flag bit is set.
The flag bits LINID, LINBK and LINHTE are reset by writing a one to the FLEX_US_CR.RSTSTA bit.
